The field of the invention relates to control systems for controlling engine air/fuel operation in response to exhaust gas oxygen sensors.
It is well-known to trim liquid fuel delivered to the engine in response to an exhaust gas oxygen sensor output to maintain a stoichiometric air/fuel ratio. Typically, the exhaust gas oxygen sensor is continuously heated to maintain operating temperature and, accordingly, a stable peak-to-peak excursion in the sensor output.
To conserve electrical power, approaches have been developed to infer the temperature of the exhaust gas oxygen sensor from engine operating conditions such as throttle position, inducted airflow, and engine speed. Electrical energy is supplied to, or decoupled from, the heater or in response to these engine measurements in an attempt to maintain constant temperature while conserving electrical power.
The inventors herein have recognized a number of problems with the above approach. For example, inferring sensor temperature from engine operating conditions may not be perfectly correlated with actual sensor temperature for all operating conditions, all vehicles, all powertrain combinations, and all exhaust gas oxygen sensors. Further, initial correlations may drift as engines, engine components, and sensors age.